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P Beck - One of the best experts on this subject based on the ideXlab platform.
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spectral investigation of ceres analogue mixtures in depth analysis of crater central peak material ccp on ceres
Icarus, 2020Co-Authors: Alicia Galiano, F Dirri, Ernesto Palomba, Andrea Longobardo, B Schmitt, P BeckAbstract:Abstract The dwarf planet Ceres is an airless body composed of Mg-Phyllosilicates, NH4-Phyllosilicates, Mg/Ca-carbonates and a dark component. The subsurface of Ceres, investigated by the material composing the peak of complex craters (ccp, crater central peak material; Galiano et al., 2019), reveals a composition similar to the surface, with an increasing abundance of Phyllosilicates in the interior. A moderate trend between age of craters' formation and spectral slope of ccps suggests that younger ccps show a negative/blue slope and older ccps are characterized by positive/red slope. To investigate the causes of different spectral slope in ccps, different grain-sized Ceres analogue mixtures were produced and spectrally analysed. First, the end-members of the Ceres surface (using the antigorite as Mg-Phyllosilicate, the NH4-montmorillonite as NH4-Phyllosilicate, the dolomite as carbonate and the graphite as dark component), were mixed, obtaining mixtures with different relative abundance, and identifying the mixture with the reflectance spectrum most similar to the average Ceres spectrum. The selected mixture was reproduced with grain size of 0–25 μm, 25–50 μm and 50–100 μm. The three mixtures were heated and spectrally analysed, both with an acquisition temperature of 300 K (room temperature) and 200 K (typical for surface Ceres temperature during VIR observations). The best analogue Ceres spectrum is coincident with a mixture composed of 18 M% (mass percentage) of Dolomite, 18 M% of Graphite, 36 M% of Antigorite and 28 M% of NH4-montmorillonite, after experiencing a heating process. The heating process produces: 1) a darkening and reddening of spectrum, as consequence of the devolatilization of OH group in Phyllosilicates and a more dominant effect of opaque phase; 2) a deepening in the intensity of the 3.4 and 4.0 μm band, as well as the 2.7 and the 3.1 μm band, likely due to the loss of absorbed atmospheric water; 3) narrowing of 3.1 μm band and the shift of band center toward longer wavelength (i.e. at 3.06 μm) coincident with mean Ceres spectrum, related to the loss of absorbed atmospheric water. The analysis of the best Ceres analogue mixture, reproduced at different grain size and after heating process, reveals a weakening of 2.7, 3.1, 3.4 and 4.0 absorption bands in coarser samples, likely related to large size of dark grains which reduce the spectral contrast. Furthermore, spectra of coarser mixtures are more red-sloped, suggesting that this trend is more affected by the dark component. The best analogue Ceres mixture produced in this work is almost coincident with the mean spectrum of Haulani ccp, the youngest ccps on Ceres and therefore representative of less altered material on Ceres. The redder spectral slope observed in the older ccps is probably the consequence of the space weathering effects on the original material composing the peak.
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The secondary history of Sutter's Mill CM carbonaceous chondrite based on water abundance and the structure of its organic matter from two clasts
Meteoritics and Planetary Science, 2014Co-Authors: P Beck, B Schmitt, E. Quirico, A. Garenne, Q. -z. Yin, L. Bonal, G. Montes-hernandez, Gilles Montagnac, R. Chiriac, F. TocheAbstract:Sutter's Mill is a regolith breccia composed of both heavily altered clasts and more reduced xenoliths. Here, we present a detailed investigation of fragments of SM18 and SM51. We have characterized the water content and the mineralogy by infrared (IR) and thermogravimetric analysis (TGA) and the structure of the organic compounds by Raman spectroscopy, to characterize the secondary history of the clasts, including aqueous alteration and thermal metamorphism. The three methods used in this study suggest that SM18 was significantly heated. The amount of water contained in Phyllosilicates derived by TGA is estimated to be approximately 3.2 wt%. This value is quite low compared with other CM chondrites that typically range from 6 to 12 wt%. The infrared transmission spectra of SM18 show that the mineralogy of the sample is dominated by a mixture of Phyllosilicate and olivine. SM18 shows an intense peak at 11.2 mu m indicative of olivine (Fig. 1). If we compare SM18 with other CM and metamorphosed CM chondrites, it shows one of the most intense olivine signatures, and therefore a lower proportion of Phyllosilicate minerals. The Raman results tend to support a short-duration heating hypothesis. In the ID/IG versus FWHM-D diagram, SM18 appears to be unusual compared to most CM samples, and close to the metamorphosed CM chondrites Pecora Escarpment (PCA) 91008 and PCA 02012. In the case of SM51, infrared spectroscopy reveals that olivine is less abundant than in SM18 and the 10 mu m silicate feature is more similar to that of moderately altered CM chondrites (like Murchison or Queen Alexandra Range [QUE] 97990). Raman spectroscopy does not clearly point to a heating event for SM51 in the I-D/I-G versus FWHM-D diagram. However, TGA analysis suggests that SM51 was slightly dehydrated as the amount of water contained in Phyllosilicates is approximately 3.7 wt%, which is higher than SM18, but still lower than Phyllosilicate water contents in weakly altered CM chondrites. Altogether, these results confirm that fragments with different secondary histories are present within the Sutter's Mill fall. The dehydration that is clearly observed for SM18 is attributed to a short-duration heating based on the similarity of its Raman spectra to that of PCA 91008. Because of the brecciated nature of Sutter's Mill and the presence of adjacent clasts with different thermal histories, impacts that can efficiently fragment and heat porous materials are the preferred heat source.
Cj Spiers - One of the best experts on this subject based on the ideXlab platform.
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Low Friction Coefficient of Phyllosilicate Fault Gouges and the Effect of Humidity: Insights From a New Microphysical Model
'American Geophysical Union (AGU)', 2020Co-Authors: Hartog Sam, Faulkner Dr, Cj SpiersAbstract:Fault slip is often localized in Phyllosilicate‐rich fault gouges in a manner consistent with the relatively low friction coefficients measured for dry and especially wet Phyllosilicates in laboratory experiments. However, the microphysics controlling these low friction coefficients remains unclear. Here, we propose a microphysical model, inspired by microstructural observations, for the prediction of the absolute value of the friction coefficient of pure dry and wet Phyllosilicates. Experimentally produced Phyllosilicate gouges suggest that shearing is controlled by sliding along (001) grain/platelet interfaces operating in series with removal of overlapping grain edge barriers by basal cleavage. We derive a model incorporating a subcritical crack propagation equation for the latter, constrained by subcritical crack growth data for muscovite. Model predictions for muscovite show similar trends regarding the effects of humidity and slip velocity on friction coefficient as do experiments at room temperature. The absolute value predicted for the friction coefficient is difficult to compare with experimental values, as it critically depends on atomic scale (001) sliding resistance, which is poorly constrained by available experimental data. Further discrepancies with experimental data can be explained by effects of varying grain size, grain aspect ratio, and porosity on the friction coefficient. While numerous qualitative explanations have been proposed previously for the low friction coefficient exhibited by Phyllosilicates, especially in the presence of water, our study provides a new step toward a quantitative, physically based model
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a microphysical model for fault gouge friction applied to subduction megathrusts
Journal of Geophysical Research, 2014Co-Authors: Sabine Den A M Hartog, Cj SpiersAbstract:A microphysical model is developed for the steady state frictional behavior of illite-quartz fault gouge and applied to subduction megathrust P-T conditions. The model assumes a foliated, Phyllosilicate-supported microstructure which shears by rate-independent frictional slip on the aligned Phyllosilicates plus thermally activated deformation of the intervening quartz clasts. At low slip rates or high temperatures, the deformation of the clasts is easy, accommodating slip on the foliation without dilatation. With increasing velocity or decreasing temperature, the shear of the clasts becomes more difficult, increasing bulk shear strength, until slip is activated on inclined portions of the Phyllosilicate foliation, where it anastomoses around the clasts. Slip at these sites leads to dilation involving clast/matrix debonding, balanced, at steady state, by compaction through thermally activated clast deformation. Model predictions, taking pressure solution as the thermally activated mechanism, show three regimes of velocity-dependent frictional behavior at temperatures in the range of 200–500°C, with velocity weakening occurring at 300–400°C, in broad agreement with previous experiments on illite-quartz gouge. Effects of slip rate, normal stress, and quartz fraction predicted by the model also resemble those seen experimentally. Extrapolation of the model to earthquake nucleation slip rates successfully predicts the onset of velocity-weakening behavior at the updip seismogenic limit on subduction megathrusts. The model further implies that the onset of seismogenesis is controlled by the thermally activated initiation of fault rock compaction through pressure solution of quartz, which counteracts dilatation due to slip on the fault rock foliation.
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fault rocks from the safod core samples implications for weakening at shallow depths along the san andreas fault california
Journal of Structural Geology, 2011Co-Authors: R E Holdsworth, Cj Spiers, E W E Van Diggelen, J H P De Bresser, Richard Walker, Leon BowenAbstract:The drilling of a deep borehole across the actively creeping Parkfield segment of the San Andreas Fault Zone (SAFZ), California, and collection of core materials permit direct geological study of fault zone processes at 2–3 km depth. The three drill cores sample both host and fault rocks and pass through two currently active, narrow (1–2 m wide) shear zones enclosed within a broader (ca. 240 m wide) region of inactive foliated gouges. The host rocks preserve primary sedimentary features and are cut by numerous minor faults and small, mainly calcite-filled veins. The development of Fe-enriched smectitic Phyllosilicate networks following cataclasis is prevalent in the presently inactive foliated gouges of the main fault zone and in minor faults cutting clay-rich host rocks. Calcite, anhydrite and minor smectitic Phyllosilicate veins are interpreted to have formed due to local fluid overpressuring events prior to, synchronous with and after local gouge development. By contrast, the active shear zone gouges lack mineral veins (except as clasts) and contain numerous clasts of serpentinite. Markedly Mg-rich smectitic Phyllosilicates are the dominant mineral phases here, suggesting that the fault zone fluids have interacted with the entrained serpentinites. We propose that weakening of the SAFZ down to depths of at least 3 km can be attributed to the pervasive development of interconnected networks of low friction smectitic Phyllosilicates and to the operation of stress-induced solution-precipitation creep mechanisms.
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velocity dependence of strength and healing behaviour in simulated Phyllosilicate bearing fault gouge
Tectonophysics, 2006Co-Authors: A R Niemeijer, Cj SpiersAbstract:Abstract Despite the fact that Phyllosilicates are widespread in fault zones, little is known about the strength of Phyllosilicate-bearing fault rocks under brittle–ductile transitional conditions. In this study, we explored the steady state strength and healing behaviour of a simulated Phyllosilicate-bearing fault rock, i.e. muscovite plus halite and brine, at room temperature, normal stresses of 1–9 MPa, atmospheric fluid pressure and sliding velocities of 0.001–13 μm/s, using a rotary shear apparatus. While 100% halite and 100% muscovite samples exhibit rate-independent frictional/brittle behaviour, the strength of mixtures containing 10–50% muscovite is both normal stress and sliding velocity dependent. At low velocities ( 1 μm/s), velocity-weakening frictional behaviour occurs, along with the development of a structureless, intermixed, cataclastic microstructure. The steady state porosity of samples deformed in this regime increases with increasing sliding velocity. We propose that this behaviour involves competition between dilatation due to granular flow and compaction due to pressure solution. Towards higher sliding velocities, dilatation increasingly dominates over pressure solution compaction, so that porosity increases and frictional strength decreases. During periods of zero slip, pressure solution compaction occurs, causing a significant strength increase on reshearing. Our results imply that cataclastic overprinting of mylonitic rocks in natural fault zones does not require any changes in temperature or effective pressure conditions, but can simply result from oscillating fault motion rates. Our healing data suggest that foliated, aseismically creeping fault segments will remain weak and aseismic, whereas segments that have slipped seismically will rapidly re-strengthen and remain in the unstable, velocity-weakening regime.
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frictional viscous flow of Phyllosilicate bearing fault rock microphysical model and implications for crustal strength profiles
Journal of Geophysical Research, 2002Co-Authors: Cj SpiersAbstract:It is widely believed that around the brittle-ductile transition, crustal faults can be significantly weaker than predicted by conventional two-mechanism brittle-ductile strength envelopes. Factors contributing to this weakness include the polyphase nature of natural rocks, foliation development, and the action of fluid-assisted processes such as pressure solution. Recently, ring shear experiments using halite/kaolinite mixtures as an analogue for Phyllosilicaterich rocks for the first time showed frictional-viscous behavior (i.e., both normal stress and strain rate sensitive behavior) involving the combined effects of pressure solution and Phyllosilicates. This behavior was accompanied by the development of a mylonitic microstructure. A quantitative assessment of the implications of this for the strength of natural faults has hitherto been hampered by the absence of a microphysical model. In this paper, a microphysical model for shear deformation of foliated, Phyllosilicate-bearing fault rock by pressure solution-accommodated sliding along Phyllosilicate foliae is developed. The model predicts purely frictional behavior at low and high shear strain rates and frictional-viscous behavior at intermediate shear strain rates. The mechanical data on wet halite + kaolinite gouge compare favorably with the model. When applied to crustal materials, the model predicts major weakening with respect to conventional brittle-ductile strength envelopes, in particular, around the brittle-ductile transition. The predicted strength profiles suggest that in numerical models of crustal deformation the strength of high-strain regions could be approximated by an apparent friction coefficient of 0.25-0.35 down to depths of 15-20 km.
Sibudjing Kawi - One of the best experts on this subject based on the ideXlab platform.
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ni Phyllosilicate structure derived ni sio2 mgo catalysts for bi reforming applications acidity basicity and thermal stability
Catalysis Science & Technology, 2018Co-Authors: Jangam Ashok, Zhoufeng Bian, Zunsheng Wang, Sibudjing KawiAbstract:In this work, Ni–SiO2–MgO materials synthesized via Ni-Phyllosilicate (PS) intermediates were explored for bi-reforming of methane (BRM) reaction. The influence of steam and reaction temperature was also investigated for the BRM reaction. Overall, the 15 wt% Ni–30 wt% SiO2–55 wt% MgO (Ni–SiO2–MgO[55]) catalyst maintained exceptional catalytic performance (CH4 and CO2 conversions were 80% and 60%, respectively) at 750 °C for 140 h with negligible carbon deposition and also showed a stable H2/CO of 2.0. The best catalytic performance of the Ni–SiO2–MgO[55] catalyst is attributed to its enhanced basicity strength, reasonable moderate acidity strength and structural stability during high temperature reforming reaction. The formation and presence of Ni–Mg-containing Phyllosilicates in fresh and reduced catalysts respectively was confirmed by TEM images and XRD analysis. The Tmax of around 750 °C in TPR profiles of Ni/SiO2–MgO catalysts further confirms the strength of interactions between Ni and SiO2–MgO support species.
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highly carbon resistant ni co sio2 catalysts derived from Phyllosilicates for dry reforming of methane
Journal of CO 2 Utilization, 2017Co-Authors: Zhoufeng Bian, Sibudjing KawiAbstract:Abstract This paper describes synthesis and characterization of Ni and Ni-Co alloy supported over SiO 2 derived from Phyllosilicates. A series of 10 wt% Ni-Co Phyllosilicate supported over SiO 2 with different Ni/Co ratio is successfully prepared by hydrothermal method where urea is used to release ammonia gradually providing a basic environment. TPR results show that adding of Co enhances the metal-support interaction. After H 2 reduction at high temperature, small and uniform Ni-Co alloy particles are well supported over silica. These catalysts are tested for dry reforming of methane (DRM) at 750 °C. The catalytic performance is highly affected by Ni/Co ratio: 10Ni and 7Ni3Co show high and stable activity for 100 h, whereas 5Ni5Co, 3Ni7Co and 10Co exhibit severe deactivation due to oxidation of metal sites. A harsher test has shown that adding of Co with a proper amount indeed can help to suppress metal sintering and carbon formation.
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a highly active and stable ni mg Phyllosilicate nanotubular catalyst for ultrahigh temperature water gas shift reaction
Chemical Communications, 2015Co-Authors: Zhoufeng Bian, Jangam Ashok, Sibudjing KawiAbstract:A Ni–Mg phyllosilcate (PS) nanotubular catalyst has been developed by introducing Mg into Ni Phyllosilicate nanotubes (PSNTs). The thermal stability is improved significantly. Furthermore, this binary metal PS nanotubular catalyst exhibits excellent activity and stability for ultrahigh temperature water-gas shift (WGS) reaction.
B Schmitt - One of the best experts on this subject based on the ideXlab platform.
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spectral investigation of ceres analogue mixtures in depth analysis of crater central peak material ccp on ceres
Icarus, 2020Co-Authors: Alicia Galiano, F Dirri, Ernesto Palomba, Andrea Longobardo, B Schmitt, P BeckAbstract:Abstract The dwarf planet Ceres is an airless body composed of Mg-Phyllosilicates, NH4-Phyllosilicates, Mg/Ca-carbonates and a dark component. The subsurface of Ceres, investigated by the material composing the peak of complex craters (ccp, crater central peak material; Galiano et al., 2019), reveals a composition similar to the surface, with an increasing abundance of Phyllosilicates in the interior. A moderate trend between age of craters' formation and spectral slope of ccps suggests that younger ccps show a negative/blue slope and older ccps are characterized by positive/red slope. To investigate the causes of different spectral slope in ccps, different grain-sized Ceres analogue mixtures were produced and spectrally analysed. First, the end-members of the Ceres surface (using the antigorite as Mg-Phyllosilicate, the NH4-montmorillonite as NH4-Phyllosilicate, the dolomite as carbonate and the graphite as dark component), were mixed, obtaining mixtures with different relative abundance, and identifying the mixture with the reflectance spectrum most similar to the average Ceres spectrum. The selected mixture was reproduced with grain size of 0–25 μm, 25–50 μm and 50–100 μm. The three mixtures were heated and spectrally analysed, both with an acquisition temperature of 300 K (room temperature) and 200 K (typical for surface Ceres temperature during VIR observations). The best analogue Ceres spectrum is coincident with a mixture composed of 18 M% (mass percentage) of Dolomite, 18 M% of Graphite, 36 M% of Antigorite and 28 M% of NH4-montmorillonite, after experiencing a heating process. The heating process produces: 1) a darkening and reddening of spectrum, as consequence of the devolatilization of OH group in Phyllosilicates and a more dominant effect of opaque phase; 2) a deepening in the intensity of the 3.4 and 4.0 μm band, as well as the 2.7 and the 3.1 μm band, likely due to the loss of absorbed atmospheric water; 3) narrowing of 3.1 μm band and the shift of band center toward longer wavelength (i.e. at 3.06 μm) coincident with mean Ceres spectrum, related to the loss of absorbed atmospheric water. The analysis of the best Ceres analogue mixture, reproduced at different grain size and after heating process, reveals a weakening of 2.7, 3.1, 3.4 and 4.0 absorption bands in coarser samples, likely related to large size of dark grains which reduce the spectral contrast. Furthermore, spectra of coarser mixtures are more red-sloped, suggesting that this trend is more affected by the dark component. The best analogue Ceres mixture produced in this work is almost coincident with the mean spectrum of Haulani ccp, the youngest ccps on Ceres and therefore representative of less altered material on Ceres. The redder spectral slope observed in the older ccps is probably the consequence of the space weathering effects on the original material composing the peak.
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The secondary history of Sutter's Mill CM carbonaceous chondrite based on water abundance and the structure of its organic matter from two clasts
Meteoritics and Planetary Science, 2014Co-Authors: P Beck, B Schmitt, E. Quirico, A. Garenne, Q. -z. Yin, L. Bonal, G. Montes-hernandez, Gilles Montagnac, R. Chiriac, F. TocheAbstract:Sutter's Mill is a regolith breccia composed of both heavily altered clasts and more reduced xenoliths. Here, we present a detailed investigation of fragments of SM18 and SM51. We have characterized the water content and the mineralogy by infrared (IR) and thermogravimetric analysis (TGA) and the structure of the organic compounds by Raman spectroscopy, to characterize the secondary history of the clasts, including aqueous alteration and thermal metamorphism. The three methods used in this study suggest that SM18 was significantly heated. The amount of water contained in Phyllosilicates derived by TGA is estimated to be approximately 3.2 wt%. This value is quite low compared with other CM chondrites that typically range from 6 to 12 wt%. The infrared transmission spectra of SM18 show that the mineralogy of the sample is dominated by a mixture of Phyllosilicate and olivine. SM18 shows an intense peak at 11.2 mu m indicative of olivine (Fig. 1). If we compare SM18 with other CM and metamorphosed CM chondrites, it shows one of the most intense olivine signatures, and therefore a lower proportion of Phyllosilicate minerals. The Raman results tend to support a short-duration heating hypothesis. In the ID/IG versus FWHM-D diagram, SM18 appears to be unusual compared to most CM samples, and close to the metamorphosed CM chondrites Pecora Escarpment (PCA) 91008 and PCA 02012. In the case of SM51, infrared spectroscopy reveals that olivine is less abundant than in SM18 and the 10 mu m silicate feature is more similar to that of moderately altered CM chondrites (like Murchison or Queen Alexandra Range [QUE] 97990). Raman spectroscopy does not clearly point to a heating event for SM51 in the I-D/I-G versus FWHM-D diagram. However, TGA analysis suggests that SM51 was slightly dehydrated as the amount of water contained in Phyllosilicates is approximately 3.7 wt%, which is higher than SM18, but still lower than Phyllosilicate water contents in weakly altered CM chondrites. Altogether, these results confirm that fragments with different secondary histories are present within the Sutter's Mill fall. The dehydration that is clearly observed for SM18 is attributed to a short-duration heating based on the similarity of its Raman spectra to that of PCA 91008. Because of the brecciated nature of Sutter's Mill and the presence of adjacent clasts with different thermal histories, impacts that can efficiently fragment and heat porous materials are the preferred heat source.
E Noe Z Dobrea - One of the best experts on this subject based on the ideXlab platform.
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mineralogy and stratigraphy of Phyllosilicate bearing and dark mantling units in the greater mawrth vallis west arabia terra area constraints on geological origin
Journal of Geophysical Research, 2010Co-Authors: Janice L Bishop, E Noe Z Dobrea, Joseph R. Michalski, N K Mckeown, R R Fu, Christopher M Rossi, C Heinlein, V HanusAbstract:[1] Analyses of MRO/CRISM images of the greater Mawrth Vallis region of Mars affirm the presence of two primary Phyllosilicate assemblages throughout a region ∼1000 × 1000 km. These two units consist of an Fe/Mg-Phyllosilicate assemblage overlain by an Al-Phyllosilicate and hydrated silica assemblage. The lower unit contains Fe/Mg-smectites, sometimes combined with one or more of these other Fe/Mg-Phyllosilicates: serpentine, chlorite, biotite, and/or vermiculite. It is more than 100 m thick and finely layered at meter scales. The upper unit includes Al-smectite, kaolin group minerals, and hydrated silica. It is tens of meters thick and finely layered as well. A common Phyllosilicate stratigraphy and morphology is observed throughout the greater region wherever erosional windows are present. This suggests that the geologic processes forming these units must have occurred on at least a regional scale. Sinuous ridges (interpreted to be inverted channels) and narrow channels cut into the upper clay-bearing unit suggesting that aqueous processes were prevalent after, and possibly during, the deposition of the layered units. We propose that layered units may have been deposited at Mawrth Vallis and then subsequently altered to form the hydrated units. The Fe/Mg-Phyllosilicate assemblage is consistent with hydrothermal alteration or pedogenesis of mafic to ultramafic rocks. The Al-Phyllosilicate/hydrated silica unit may have formed through alteration of felsic material or via leaching of basaltic material through pedogenic alteration or a mildly acidic environment. These Phyllosilicate-bearing units are overlain by a darker, relatively unaltered, and indurated material that has probably experienced a complex geological history.
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hydrated silicate minerals on mars observed by the mars reconnaissance orbiter crism instrument
Nature, 2008Co-Authors: John F Mustard, S L Murchie, S M Pelkey, B L Ehlmann, R E Milliken, John A Grant, J P Bibring, F Poulet, Janice L Bishop, E Noe Z DobreaAbstract:Phyllosilicates, a class of hydrous mineral first definitively identified on Mars by the OMEGA (Observatoire pour la Mineralogie, L'Eau, les Glaces et l'Activitie) instrument, preserve a record of the interaction of water with rocks on Mars. Global mapping showed that Phyllosilicates are widespread but are apparently restricted to ancient terrains and a relatively narrow range of mineralogy (Fe/Mg and Al smectite clays). This was interpreted to indicate that Phyllosilicate formation occurred during the Noachian (the earliest geological era of Mars), and that the conditions necessary for Phyllosilicate formation (moderate to high pH and high water activity) were specific to surface environments during the earliest era of Mars's history. Here we report results from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) of Phyllosilicate-rich regions. We expand the diversity of Phyllosilicate mineralogy with the identification of kaolinite, chlorite and illite or muscovite, and a new class of hydrated silicate (hydrated silica). We observe diverse Fe/Mg-OH Phyllosilicates and find that smectites such as nontronite and saponite are the most common, but chlorites are also present in some locations. Stratigraphic relationships in the Nili Fossae region show olivine-rich materials overlying Phyllosilicate-bearing units, indicating the cessation of aqueous alteration before emplacement of the olivine-bearing unit. Hundreds of detections of Fe/Mg Phyllosilicate in rims, ejecta and central peaks of craters in the southern highland Noachian cratered terrain indicate excavation of altered crust from depth. We also find Phyllosilicate in sedimentary deposits clearly laid by water. These results point to a rich diversity of Noachian environments conducive to habitability.
